Drivers are needed for the transportation of oblong test samples through a material testing device, such as eddy-current or stray-flux testing equipment, where it is important to have within a relatively large diameter range, uniform axial movement of the test samples and to be able to guide them accurately along a given track through the testing device, irrespective of diameter variations or cross movement of the driven material.
A driver for this purpose is known which has three arms movable over a lifting spindle in radial direction of the test material and exhibiting at their front end each a fork accommodating a driving roller. The axles of the driving rollers are driven by a common geared motor through drive shafts, the upper roller for space reasons, requiring an additional miter gear. The lifting spindles are actuated by a common control mechanism. The disadvantage of such a driver is that the three drive shafts are arranged in different directions outwards and terminate at positions remote from each other. Their common drive, therefore, requires a complicated and expensive gear arrangement. Another disadvantage is that for radially set rollers, the useful diameter range is restricted with respect to small diameter test material for the rollers cannot come together sufficiently close enough, even when a sharp-angled roller profile is used instead of the more typical right-angle profile. A further disadvantage is that a common actuation of three lifting spindles located relatively remote from each other is not possible without appreciable mechanical effort.